Two-way radio system



Patented Nov. 18, 1947 TWO-WAY RADIO SYSTEM Ralph A. Varone, Audubon, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application August 4, 1945, Serial No. 608,949

(Cl. Z50-13) 8 Claims.

This invention relates to two-Way radio systems and is particularly directed to the wave generating equipment to be used therein.

It is important that reception and transmission in a two-way radio system shall be maintained with a high degree of frequency stability in respect to the carrier wave. It is important also that a superheterodyne receiver be controlled by a local oscillator having the greatest possible frequency stability.

It is, therefore, an object of my invention to provide a two-way radio system having generator equipment capable of a high degree of frequency stability and adjustably tunable within a wide range of frequencies.

Another object of my invention is to provide a two-way radio system in which a radio frequency amplifier and converter may be used in common by the transmitting and receiving equipment.

Still another object of my invention is to provide generator equipment in which a crystalcontrolled high frequency generator is used in combination with a variably tunable low frequency oscillator to obtain a heterodyne frequency which may be continuously varied over a relatively wide range of frequencies.

Other objects and advantages of my invention will be brought out in the more complete description to follow. This description is accompanied by a drawing in which Figure 1 represents diagrammatically a practical circuit arrangement for carrying out the invention, and Figure 2 shows an inductive interstage coupling arrangement which may be preferred in place of a more direct coupling shown at one part of Figure 1.

Referring to Figure 1, I show therein a crystal controlled oscillator comprising an electron discharge tube I which is preferably of the pentode type having a cathode 2, an anode 3 and three grids numbered respectively 4, 5 and 5. In a connection between the cathode 2 and ground is a tunable resonant circuit comprising an adjustable capacitor 'I in parallel with the primary winding 8 of a transformer 9. 'Ihe secondary l of this transformer is coupled to the primary winding Il of another transformer I2.

The anode 3 is supplied with positive potential from any suitable direct current source indicated as +B. Connection of the anode to this source is made through a. resistor I3. The screen grid is also connected to the source through a suitable resistor I4. The screen grid is coupled to ground through a capacitor I5 in order to bypass unwanted frequency components.

The control grid 4 is grounded through a circuit which includes a grid resistor I6. Grid 4 is also coupled to ground through a circuit which includes a piezo-electric crystal I'I in series with a capacitor I8. A capacitor I9 serves to bypass unwanted frequencies to ground as they may appear on the anode 3.

The circuit arrangement described in the foregoing paragraphs is that of a more or less conventional crystal oscillator. The output is fed to the transformer I2 the secondary winding 20 of which has its two terminals connected respectively to separate grids 2l in a twin triode discharge tube 22. A center-tap on the transformer Winding 20 is connected to one terminal of a secondary winding 23 in a transformer 24. The primary winding 25 of this transformer forms the inductance of a tunable resonant circuit. Tuning of the circuit is accomplished by permeability tuning. The parallel capacitance of this circuit includes an adjustable capacitor 26, and a fixed capacitor 26a. The adjustable capacitor is used for setting the circuits to calibration at the low frequency end of the band.

The input circuit for tube 22 may be traced from the grids 2l through the two ends of the secondary winding 20 to its center tap and thence through the secondary winding 23 to ground. The common cathode in tube 22 is connected to ground through a resistor 21. This resistor is shunted by a capacitor 28.

A low frequency oscillator variable within a considerable range of frequencies is shown to include a. triode discharge tube 29. The cathode 30 of this tube is grounded. Its control grid 3l is connected to the grounded cathode through a resistor 32. Control energy is fed to the grid 3| through a circuit which includes a tap 33 on the permeability tuned inductance 25 of the resonant circuit, this tap being coupled to the 1 grid 3| across a capacitor 34. Anode potential is supplied to the anode 35 from the-l-B source which in this case is fed through a resistor 36 to a tap 31 on the permeability tuned inductance 25.

The circuit which includes tube 22 will be recognized by those skilled in the art as a balanced modulator. The output from the crystal oscillator is fed to the grids 2I in push-pull. That is, the two grids are excited out of phase with each other. In the output circuit which includes the two space paths of the twin triode tube 22 and the primary winding of a transformer 38 it will be observed that the even harmonics of the crystal oscillator frequency are substantially suppressed.

From the foregoing observations it will be understood that the output circuit from the balanced modulator will contain current at the frequency of the crystal oscillator (fe) and heterodyned With frequency components of frequencies resulting from the combined outputs of the two generators. These components may be represented as (ft-ifo). Tuning elements Ce and Lc a main tuning condenser 39 and a Vernier con;H l denser 40. This resonant circuit is tuned to either y of the frequencies (fc-I-fo) or (fc-fo). The balanced modulator circuit makes possible the suppression of even harmonics of the frequency fc and odd harmonics of the frequency fo. It is, however, possible to interchange the connections between the oscillators and the transformer I2 so that frequency fc may be applied in push-push and frequency fo may be applied in push-pull.

To continue with the `circuit description: The output from the transformer 38, or from transformer 38a (Fig. 2), is fed across capacitors 4| and t2 to the control griddS in a discharge tube All which'may be used if desired as a single side band frequency multiplier. Tube dll has a conventional input circuitv including a grid resistor v45 and a cathode resistork t6, the latter being shunted by a capacitor 41. Elements 45, 46 and 41 are all grounded at one end. The anode 4S is connected to the positive terminal of the direct current source -l-B through a resistor' 49 in series with the primary winding 50 of an output transformer 51. This primary winding constitutes the inductan'ce of a tunable resonant circuit the capacitiveelements ofwhich are shown as a' main tuning condenserand a Vernier ccndenser52. Condenser 53 and resistor d'9 act as a decoupling network isolating resonant circuit 5Fl,V 5l from the +B connection. IThe screengrid 5A is supplied with suitable positive `potential from the +B -source fed througha resistorf55, Unwanted frequency components appearing on the screen grid '541 vare bypassed to ground through a capacitor 55.

As shownV in Fig. 2 the primary winding of transformer SB may be inductively coupled -to the input side vof a lter network F if desired. This network -includes'a -shunt inductance Lc in series with ashunt capacitance Cc. The output side of this'v network iscoupled-through atransformer 38a to thetuned circuitcomprising elements` 39, ci? and ifi!y as shownin Fig .l.1. Y

It will be 4understoodthat the resonant circuit including inductance 5and capacitance 5| may be tuned to .anydesired multiple frequency with respect to the output from 'the balanced modulat'or stage. In other words, Tthe output 'fed across the transformer 51 is that 'which is selected by the resonant frequency of the `tuned circuit 5U, 5|.

This resonant circuit and `its associated tube 44 l is thus constituted as a multiplier stage operating on'one 'of the 'side bands vproduced in Abalanced modulator 22, the loutput thereofV beingsuitable for use both for transmission yand for reception,

but 'is preferably tuned to a frequency-Which may -be heterodyned rwiththe received carrier wave -todeliver the xedY frequency of the I. F. ampliiier in the receiver.

The-secondarywindingfSB in transformer 51 Vis grounded at one end fand is `connected at the other end to aswit'ch blade 55 ina four-poledouble-throw switch. When the blades 'of this `switch are thrown to the left (points T) they -are `in Vposition'forutilizing the transmitter of the two-way rradiosystem. `-When the switch blades are thrown to the right (points R) -they are in position for reception.

A frequency converter unit `is shown having a ldischarge tube BI `which `includesa cathode 62,

an Aanode and a' multiplicity of grids. The

4 purpose of this tube is to generate oscillations which may be mixed with the frequency derived from the hereinbefore describedmultiplier stage "dit When this convert-erk stage is used a carrier frequency fs may be derived according to the formula fszmfcfwifif. The frequency fif is to be that of an intermediate frequency amplifier B2 which is used in the receiver section. A resonant circuit composed of an inductance 63 in paralle1 with an adjustable capacitor 64 is inserted between the cathode 62 and ground. This frequency fi: is maintained constant by means of a piezo electric crystal `61 having substantially the same natural frequency, The control grid S5 is connected to ground through a resistor 6B. The piezo electric crystal 61 is in shunt with this resistor.

The second control grid 58 :is connected to ground through a resistor'SS and receives control potentials from the frequency multiplierstage across a coupling capacitor Si). Directcurrent potential is supplied to the anode 10 througha resistor-il leading to the positive terminal, -l-B, of the vdirect current source. Screengrid potential for the second and fourth `grids linY the tube 5l is applied from the direct current source through resistor 12. The output. from thereonverter tube 6l is coupled across a capacitor 13.to

the input circuit of azc'onventional radio fre-` quency amplifier unit 14, whichzis tunedv to the carrier frequency fs to be used for transmission vand reception.

The purpose of the fourepole-double-throw switchv is to provide alternative use of thertransmitter section and the receiver section respectively. Assuming that the. switch blades of this four-pole-doubleethrow switch areV moved t0 the left, that is onto contact. points T, then the transmittersection will nbe utilized asifollows: The carrier frequency fs is Lcon-ducted across capacitor 13 to switch blade 18 and thence to the input side of the radio frequency amplifier 14, this-amplifier being tuned to the 'frequency fs. Theoutput from the RF amplifier is then fed through switch blade t() toa buffer amplier unitGS -a-n'd thence to a modulated power a-mplier. -A microphone or other source of intelligence Ysignals y11 is used to controlan audio amplifler81 the output from whichv is fed to the Ymodulated powery amplifier unit 86. In placeof the microphonelany'suitable source 'of intelligence'signals may-be employed, such as a telegraph keying` device (whether manual or automatic), a facsimile transmitter or a television transmitter.

'The carrier frequency Vand the modulation signals are combined in 'the unit `86 andthe output Vis fed to an antennacoupler' 8'8. `The output'from the coupler unit is then fed throughfswitch blade -15 to the antenna and is. radiated for purposes of transmission.

switch blade 59 to the receiver` converter .'unitl where it is combined with the incoming modulated carrier wave from the antenna 16 now connected through switch blade to its R contact. This contact is directly connected to the input side of the R. F, amplifier 'M The output from unit 14 is now connected through switch blade 80 to the receiver converter 8l. Accordingly, the incoming signals are amplified, heterodyned with the local oscillations and fed through the I. F. amplifier 82 to a detector and audio amplifier 83. This last mentioned unit supplies output energy to a loudspeaker 84 or other translating device.

In order to increase the frequency range of the wave generating equipment without appreciable sacrifice in its stability it is, of course, to be understood that I may provide facilities for convenient interchange of crystals in the place of crystal Il.

If four crystals are taken and cut to oscillate at the following frequencies 2000 kc., 2300 kc., 2600 kc., and 2900 kc.

it will then be seen that they cover four frequencies from 2000 to 2900 kc. If each of these crystals one at a time is heterodyned with a variable frequency oscillator of say 600 to 900 kc., then it is possible to utilize the side bands of the two beating oscillators. Let us assume that the upper side bands are utilized for purposes of this discussion. A variable range of frequencies is then available with an increment of 300 kc. for the selectionof each crystal. The new band of frequencies now available is:

2000 kc. crystal 2600 to 2900 kc.

2600 kc. crystal 2900 kc. crystal 3200 to 3500 kc. 3500 to 3800 kc.

Hence a band of frequencies that are continuously variable are now available in the range of 2600 to 3800 kc. The total increment is 3800-2600=1200 and that is equal to 4 300 when 300 kc. is the increment of the variable frequency oscillator.

For each combination of one crystal and the variable frequency oscillator f1=(fifo).

Now if the side band obtained by heterodyning is multiplied by a frequency multiplier then a new band of frequencies is available with a given set of crystals. This new band of frequencies will be related to the original by a multiplying factor (n) which may be 1, 2, 3, 4, etc. If the original band has a continuous range, then all other bands multiplied by the factor (n) will be continuous. Therefore, it is possible to select a number of crystals and a variable frequency oscillator and gencrate a continuous range of frequencies. It is merely required that the frequency increment covered by the variable frequency oscillator be equal to the difference frequency between crystals. I-Ience a general expression for the frequency may be written,

2300 kc. crystal 2900 to 3200 kc.

Where,

f is the generated frequency fc is the crystal frequency fo is the frequency of the variable oscillator n is the multiplying factor 1, 2, 3, etc.

In Equation 1 (i) sign is used to include both side bands, the upper and lower.

If fo, the frequency of the variable frequency oscillator is made a small percentage of fc, the crystal frequency, then the frequency stability of f approaches the stability of the crystal.

The selection of a desired multiple frequency to be used in the frequency multiplier unit is readily made by use of gang control of certain tuning Condensers. These Condensers 39 and 5| and a tuning condenser (not shown) within the R. F. amplier unit 14 may all be ganged together. Condensers 4| and 52 are used as tracking condensers. r

Various modifications of my invention may, of course, be made without departing from the spirit and scope as will be understood by those skilled in the art. For example, in place of a frequency multiplier operating on one of the side bands produced in modulator 22, I may, if desired, employ a regenerative frequency multiplier unit having balanced discharge devices, the controlled grids of which would be conventionally connected to the -secondary terminal of an output transformer While the anode of the two discharge devices would be connected in parallel to the output circuit. Other modifications will, of course, suggest themselves to those skilled in the art.

What is claimed is: 1. In a two-way radio system, a wave generator having three primary sources of oscillations for producing respectively the frequencies fc, fu and fr, piezo-electric devices respectively in circuit with the sources fc and fi for stabilizing their frequencies, means for varying the frequency fo within a limited range, a converter for combining the outputs from sources f and fo thereby to obtain the frequency Vfair, means for deriving therefrom a multiple frequency mfcifo), a radio frequency amplifier tuned to a frequency fs which is equal to the sum or difference frequency dened by the formula fs=n(fe i:fo)iff, a transmitter including means for modulating a wave of frequency fs derived from the mixture of wave energy from the three said sources, the output side of said amplifier being connectable to cascaded amplifier and mixer stages in said transmitter, a receiver including means responsive to an incoming modulated wave fed through said amplifier for heterodyning the same with energy of the frequency mfcifu) which is obtained as output from said multiple frequency deriving means, and switching means for utilizing said transmitter and receiver alternatively.

2. The combination according to claim 1 in which said switching means is constituted as a four-pole-dobule-throw switch.

3. A signaling system comprising an antenna, a transmitter, a receiver having an intermediate frequency amplifier therein, a radio frequency amplifier common to the transmitter and the receiver, switching means providing circuit connections from said antenna through said ampliiier to the receiver for producing a response to incoming signals, said switching means also providing circuit connections for operation of said transmitter and for feeding modulated signal energy therefrom to said antenna, three local oscillators of which two are crystal-controlled and the third is tunable over a. predetermined frequency band, means for deriving a carrier wave bythe mixing and filtering of energies derived from the three said oscillators for use in said transmitter, and means for mixing the wave output from the tunable oscillator and one of the crystal oscillators and for heterodyning a derivative therefrom with incoming signal energy to obtain an intermediate frequency acceptable to said intermediate frequency amplifier in said receiver.

4. In a system adapted to transmit and to receivesignalsv onv the same carrier Wave fs, means for. generating two Waves of; frequencies-fg. and fe, respectively, means forl deriving from the. Qutputs of said generating means a multiple frequency nfcife), an oscillator converter stage into which energy of the frequency nifeija) is injected from said means for deriving that frequency, the; 0111iput from said stage being of a frequency fgvvhich satisfies the formula fi.:.famillievije),` an amplier tuned to the frequencyY je a transmitting circuit arrangement including means for medulating and further amplifying the output from said amplier of the frequency fs, vand a receiving eircuit errangement` including. a, @n-verter, an I. F- amplifier tuned to the frequency fi, a detectoraudio-amplifier and translating device, Ysaid receiver being arranged to mix the locally derived Wave of frequency Mfcifo) with an incoming modulated wave of frequency fsA to derive the frequency f1.

plying and mixing electr-ical waves, of several different frequencies for use both in the transmission and in the reception of radio signals., said method comprising generati-ng and mixing two waves to derive a Wave of the frequency fcifo,

Where fc and fo represent the outputs from a frequency-stabilized oscillation generator and a varialcle frequency generator respectively, multiplying the derived Wave by a factor n to obtain Ya Wave of frequency mici-fo), generating a Wave of frequency fr and mixing the same with said wave of multiplied frequency to obtain avvave of frequency fs which equals mietje) ijn transmitting signals which are characterized as modulated `signal energy having a carrier component of the frequency fs, and receiving modulated signal energy so characterized when that energy is heterodyned with a wave of frequency mfc-LIQ) to produce an intermediater frequency Wave fi.

6. The method according to claim in combination With processes of filtering out unwanted harmonic components of the Waves offrequenrcies fc and fn, thereby to purify the utilized carrier Wave component fs, and the Wave of frequency mfeifo) when used for heterodyne reception.

'Ehe method, of; generating frequency multi.- niyingand` mixing electrical Waves ofv several diiferent frequencies for use both in the transmission and in the reception of radio signals, said 5 method comprisingy generating and, mixing two Waves of frequencies fc and fo respectively to derive a. beat'frequenc-y Wave of the frequency [e-.l-fo, multiplying the derived beat Wave, generating a wave of frequency fr and mixing thev same 1 0 with said Wave of multiplied frequency to obtain a Wave of frequency fs, transmitting signals Which are characterized as modulated signal energy having a carrier component of the frequency fs, and receiving modulated signal energy so characterized that when said signal energy is heterodyned with said multiplied Wave an intermediate frequency Wave f1 is produced- 8. The method of generating, frequency multiplying and mixing electrical Waves of several dif- ;0 ferent frequencies for use both in the transmis- 5. The method of generating, frequency vmultision and in the reception of radio signals, said method comprising generating and mixing two waves to derive a beat frequency Wave, multiplying the ,derived beat frequency wave, generating ,25 a fourth Wave and mixing the samewith said wave o f multiplied frequency to obtain a fifth wave, transmitting signals which are characterized asV modulated signal energy having a carrier QQmDOnent of the frequency of .said fifth wave and receiving modulated signal energy so characterized that when signal energy is heterodyned with a. Wave of the frequency of said multiplied Wave an intermediate frequency wave of a frequency equal to said fourth Wave is produced.

RALPH A. vARoNE.

REFERENCES CITED The following references are of record in the D le of this patent:

.UNITED STATES PATENTS Numberv Name Date 2,398,694 Case i Apr, 16, 1946 Vogel Oct. 8, V1946 McRae r Apr, 27, 14943 

